Breakdown of qualitative leaf rust resistance in the wheat cultivar 'BRS 194' by a new race of Puccinia triticina/Superacao da resistencia qualitativa da cultivar de trigo 'BRS 194' por uma nova raca de Puccinia triticina

• Published in: Ciência rural 2009-01, Vol.39 (1), p.228
• Main Authors: Chaves, Marcia Soares, Wesp, Caroline de Lima, Barcellos, Amarilis Labes, Scheeren, Pedro Luiz, Silva, Marcio So, Caierao, Eduardo
• Format: Article
• Language: Portuguese
• ISSN: 0103-8478

The population of Puccinia triticina, the causal agent of wheat leaf rust, is extremely dynamic in the South Cone region of South America, where the appearance of new races is frequent. The wheat cultivar 'BRS 194' was the second variety in availability of seeds for planting in Rio Grande do Sul and Santa Catarina States in 2005, because it has good agronomic characteristics as rusticity, high yield and resistance to all races of P. triticina occurring in Brazil and other countries in South America. In 2005, pustules of leaf rust were observed in this cultivar on farms and in experimental fields, indicating the probable breakdown of its resistance. The objective of this research was to identify the race of P. triticina present in samples from 'BRS 194' and verify if it was a new virulence of the pathogen able to overcome its resistance. Eight samples of leaf rust from 'BRS 194' were sent to Embrapa--National Wheat Research Center, Passo Fundo, Brazil for isolation and identification in International Sets of Differential Hosts specific for this pathogen. All samples showed the same virulence combination, which corresponded to MFP-CT according to the North-American System of nomenclature for the pathogen's races. That was the first time that this letter code was detected in Brazil, characterizing the emergence of a new race of P. triticina virulent to 'BRS 194'. Other popular varieties were inoculated with the new race, some were susceptible and others were resistant. Among the resistant cultivars were 'Fundacep 30' and 'IPR 84', which also remain resistant to all races of the pathogen occurring in Brazil. Key words: Triticum aestivum, virulence, race-specific resistance. A populacao de Puccinia triticina, agente causal da ferrugem da folha do trigo, e extremamente dinamica na regiao do Cone Sul da America do Sul, onde o surgimento de novas racas e frequente. A cultivar de trigo "BRS 194" foi a segunda variedade com maior disponibilidade de sementes para plantio no Rio Grande do Sul e em Santa Catarina em 2005, por apresentar caracteristicas como rusticidade, elevado rendimento de graos e resistencia qualitativa a todas as racas de P. triticina ocorrentes no Brasil e em outros paises da America do Sul. Em 2005, pustulas de ferrugem da folha foram observadas sobre plantas desta cultivar, tanto em lavouras quanto em campos experimentais, indicando a possivel superacao de sua resistencia. O objetivo deste trabalho foi identificar a raca de P. triticina presente